A head-mounted display (HMD) is a device with which a user can view an image while closely wearing the same over both of his/her eyes. The head-mounted display has been widely used because it is worn individually, has a small size, and provides a wide viewing angle.
In addition, the head-mounted display is a device that enlarges an image displayed on a display device, such as an LCD or a CRT, using an optical system and shows the enlarged image to the user. The head-mounted display needs to focus on a very short distance because an image screen thereof is located very close to the eyes, and also requires very precise optical devices in order to inhibit eye fatigue.
A conventional head-mounted display is disclosed in Korean Patent Laid-Open Publication No. 10-2013-0037344. The conventional head-mounted display is a wearable display system that displays an input image signal, and includes an object lens that enlarges the image signal, a diffractive lattice that diffracts the image signal enlarged via the object lens to a predetermined angle, a wave guide that propagates the signal diffracted by the diffractive lattice, and an eye lens that forms an image of the image signal propagated through the wave guide so as to allow a user to view the image. The conventional head-mounted display may obtain a high-magnification image by primarily enlarging an image to be displayed by a refractive lens and secondarily enlarging the image by an eye lens, and may maximize the user's visual field.
However, when a user wearing glasses wears the head-mounted display, the user may feel uncomfortable. Meanwhile, when a user with poor eyesight wears the head-mounted display only, the user may not view a clear image.